The invention arose during development efforts relating to a marine drive two lever remote control, particularly to prevent shifting to forward or reverse at high engine speed, and also to permit emergency shifting when needed, even at high engine speed.
Marine drive twin lever remote controls are known. One lever is a shift lever and controls the transmission, clutch or other shift mechanism that allows changing the propeller rotation direction to provide forward, reverse or neutral boat motion. The other lever is a throttle lever and controls engine speed. In some installations, these two levers can be operated independently, which can result in damage to the boat drive transmission if the control is improperly operated. If the boat operator is inexperienced or inattentive, he may forget to reduce the engine speed by moving the throttle lever prior to shifting the transmission with the shift lever. Depending on the design of the transmission or shift mechanism, this shifting at higher than recommended engine speed can damage the transmission or cause extreme wear.
In the present invention, an interlock device is included in a dual lever remote control, and will prevent the boat operator from shifting the transmission at too high an engine speed. In the preferred embodiment, the interlock mechanism, attaches to the control at otherwise unused cable attachment points. Twin lever controls typically have two attachment points on each lever to allow attaching the control cable to one point or the other to obtain the desired cable direction (push or pull) to control various engine and transmission models. The interlock includes a pair of link rods attached to the otherwise unused attachment points. The rods pass through and are guided by a guide member mounted to the control body frame. The rod attached to the throttle lever has a notch in the side corresponding to proper engine speed for shifting without damage. The rod attached to the shift lever has three notches in the side along its length corresponding to forward, neutral and reverse shift positions. A spherical ended shuttle pin, or a pair of balls, located in the center of the guide between the rods controls the relative motion of the rods and thus the two control levers. The length of the shuttle pin is such that both rods cannot move freely at all times. One of the rods must be positioned so that the shuttle pin falls into one of its notches before the other rod can be moved freely. The shift rod cannot be moved from one shift position to another unless the notch in the throttle rod is lined up with the shuttle pin allowing the shuttle pin to move sideways and make room for the shift rod to move. This constrains shifting to low engine speed or idle range as defined by the length of the throttle rod notch Threaded rod ends facilitate adjustment as needed to set the maximum engine speed for shifting and to synchronize the notches in the link rods with the shift positions in the transmission.
The invention also includes an override. In some boating situations, particularly with inexperienced operators or in an emergency situation with experienced operators, the interlocking of the shift and throttle functions may be undesirable. The only method of rapidly reducing the boat's forward speed is to shift the transmission into reverse and increase engine speed to use reverse propeller thrust to slow the boat. With an interlock installed in a two lever remote control, the only way to accomplish this is to move the throttle lever to idle position, move the shift lever from forward through neutral into reverse, and then advance the throttle again as needed to slow the boat. This sequence of three operations may not be easily carried out by an inexperienced operator suddenly confronted with the need to quickly stop or slow the boat. The inexperienced operator's tendency may be to pull on only one lever. If the throttle lever was the only grabbed and pulled to idle, then at least the forward speed would be reduced, although not as rapidly as it would be if followed by shifting to reverse and then increasing engine speed again. If the shift lever was the one grabbed and pulled, and the control had an interlock installed, the shift lever would not move. The two lever remote control would be functioning as designed, i.e. the intention being to prevent damage to the transmission. However, the boat would continue to maintain speed without slowing.
Since a transmission will generally tolerate a few shifts at high engine speed without damage, or at least without ceasing to function, it is considered desirable to permit a high engine speed shift if it is necessary to prevent greater property damage or personal injury. To allow for this situation, the present invention includes an override in addition to the interlock. The interlock prevents the noted shifting upon application of normal force by the operator. However, upon application of abnormally high force, e.g. when applied by an operator in a panic or emergency boating situation, the override feature enables the desired shifting.
In the preferred embodiment, one of the guide passages for the link rods is transversely widened, and the link rod can move sideways if not for an external U-shaped spring holding it in position. If enough force is applied to the shift lever, the cams or ramps of the notches on the shift rod will force the throttle rod sideways by bending and flexing the spring outwardly. This will allow moving the shift rod even though the throttle rod is not in the low engine speed position that normally allows shifting. The U-shaped spring prevents overriding the interlock with normal operating force, but allows such overriding upon application of abnormal force, i.e. force as might be generated by an operator in an emergency or panic boating situation.